Three-electrode spark gap device for switching high current intensities under high voltage



J. C. DUBCIS E SPARK GAP DEVI INTENSITIES UND Nov. 24, 1970 CE FOR S EH HIGH THREE- L C R D CHING HIGH AGE 3 Sheets-Sheet 1 Filed June 25, 1968 INVENTOR JEAN 'cmuae DUBG/S ATTORNEY.

J. C. DUBOIS Nov. 24,1970

THREE-ELECTRODE SPARK GAP DEVICE FOR SWITCHING HIGH CURRENT INTENSITIES UNDER HIGH VOLTAGE 3 Sheets-Sheet 2 Filed June 25, 1968 Fug: '2, INVENTOR flak g .rzn/v (LA 11 05 ATTORNEYS Nov. 24, 1970 J. c. DUBOIS THREE-ELECTRODE SPARK GAP DEVICE FOR SWITCHING HIGH CURRENT INTENSITIES UNDER HIGH VOLTAGE r'iled June 25, 1968 INVENTOR 7 4 (M no: Ou 130/5 ATTORNEYS United States 3,543,075 THREE-ELECTRODE SPARK GAP DEVICE FQER SWITCHING HIGH (IURRENT INTENSETIES UNDER HIGH VOLTAGE Jean Claude Dubois, Royan, France, assignor to Institut Francais du Petrole, des Carburants et Luhrifiants, Rueil-Malmaison, Hauts-de-Seine, France Filed June 25, 1968, Ser. No. 739,715 Claims priority, application France, June 29, 1967,

rm. Cl. HOlj 17/06, 17/10, 17/46 US. Cl. 313-197 5 Claims ABSTRACT OF THE DISCLOSURE A three-electrode spark gap device, for closing a circuit which is connected with a very high voltage electric generator and in which a very high intensity is established. The spark gap device comprises a cylindrical anode electrically connected to a terminal of the generator, a cathode having shape of a cylindrical ring surrounding and coaxial with the anode. The cathode includes on its internal wall radial extensions formed of partitions each terminated by a plate. The spark gap device also includes at least one striking electrode located in the space limited bv the two radial planes passing along the edges of two consecutive plates and by the annular segment of the cathode between these plates. The striking electrode being more particularly located in the space limited by the annular segment, the radial planes and the plates and being connected with a generator providing a shock voltage.

When it is wished, for example, to suddenly discharge a condenser charged at a high voltage into an electric circuit where a very high intensity is generated, the closing of the circuit is generally efiected by means of a spark gap device.

In a spark gap device of conventional type, the switched voltage is applied between two electrodes (anode and cathode), called main electrodes, which have such a spacing that the field prevailing between these electrodes is lower than the disruptive level, so that no spark is produced between these electrodes.

A third electrode, called striking electrode, located in the vicinity of one of the main electrodes is supplied with a high voltage. This high voltage strikes between this third electrode and either the two main electrodes a spark which generates an ionized cloud lowering the disruptive level, i.e. the critical threshold under which no spark is produced, thereby allowing the electric discharge to build up between anode and cathode.

In most conventional spark gap devices, there is used electrodes either of hemispherical shape, or constituted of plane plates, or also of stackings of plates. 2

The known art in this matter may be illustrated by the three-electrode spark gap device described in the book High Voltage Laboratory Technique by Craggs and Meek, published by Butterworths Scientific Publications, London (see-page 180-Figure 173).

However such spark gap devices do not exhibit a structure which is strong enough to withstand the very high current intensities flowing through the device.

The object of the present invention is to realize a new three-electrode spark gap device for switching very high current intensities under high voltage, such conditions being for example encountered during the operation of a seismic sparker.

This spark gap device has a strong structure, provid ing broad electrode areas, a good thermal dissipation 3,543,075 Patented Nov. 24, 1970 and a good mechanical resistance to the acoustical shock Wave generated at the instant of striking.

Such a spark gap device has a coaxial structure. Its anode is a smooth metallic cylinder located within the cathode. The latter has the shape of a hollow cylinder, the annular internal wall of which has radial extensions along generatrices of the cylinder. The striking electrodes are constituted by rods located in the intervals separating the radial extensions of the cathode, each electrode having its own energizing circuit.

The spacing between anode and cathode will preferably be higher than 1.5 times the disruptive distance.

The present invention will be described more in detail with reference to the attached drawings, wherein:

FIG. 1 diagrammatically shows a three-electrode spark gap device combined with an electric circuit.

FIG. 2 diagrammatically shows a perspective view of a spark gap device according to the invention.

FIG. 3 is a view of the spark gap device shown by FIG. 2, together with its energizing device.

FIG. 4 illustrates a longitudinal sectional view of a part of the device of FIG. 3, provided with a three-stage anode.

Referring first to FIG. 1 showing the general diagram of a circuit for energizing a three-electrode spark gap device, such a circuit includes a high voltage generator G connected with a condenser C, a resistance R, a three-electrode spark gap device E, the two main electrodes of which p and 1 are supplied with high voltage by the condenser C, and the striking electrode a is supplied with a shock voltage emanating from a source I. The spark gap device E controls the operation of an electrical apparatus A, which may be for example a seismic sparker.

The electrodes p and p are spaced by a distance which is slightly higher than the spacing creating the disruption, so that no spark is directly generated between these electrodes.

The condenser C being charged no spark is thus produced directly between p and p but when the electrode a is supplied with a shock voltage there is generated a spark between the striking electrode a and either the two electrodes p and 2 This spark ionizes the space where it is generated making it conductive, thereby striking a passage for very high intensity current between the two electrodes 1 and p and allowing an instantaneous actuation of the apparatus A.

Referring now to FIG. 2 which illustrates, by Way of example, a preferred embodiment of the spark gap device according to the invention, this device includes in particular an anode 1 which is a cylinder made of a metal having a good electrical conductivity.

Its cylindrical wall is plated with a metal having a high melting-point, such as for example tungsten.

The cathode 3 has the shape of a cylindrical ring 4 having substantially the same length as the anode which it surrounds, being coaxial with this anode.

This cathode is provided with radial extensions on its internal wall, located at regular intervals. These extensions are constituted by partitions 5 secured to the cylindrical ring 4 along generatrices thereof, each of which being provided with a plate 6 at its end.

The internal surface of these plates is incurved so as to constitute a portion of a cylinder centered on the axis of symmetry of the system. The spacing between these plates is substantially equal to their width. This surface is coated with a refractory metal, for example with tungsten. The cathode as a whole is made of a metal which is a good conductor of electricity.

The striking or control electrodes 2 are constituted by tungsten rods having a diameter between 2 and 3 mm.

and substantially the same length as the anode and the cathode. Each of them is located in the space limited by two radial planes containing the edge 6a of two consecutive plates, on the one hand, and the annular segments of the cathode located between said radial planes, on the other hand. More particularly, those striking electrodes will be located in the space limited by these annular segments, said radial planes and the plates 6, and located along generatrices of a cylinder the axis of which is that of the device.

The electrical connection of the anode is made along the axis of this electrode by means of a cable 7 (FIG. 3) connected with one of the terminals of a capacity (not shown) charged under a very high voltage.

The electrical connection of the cathode is made by means of a shell 8 having a cylindrical internal wall in contact with the external wall of the cathode. This shell is made of a metal which is a good conductor of electricity and is thick enough to provide for a good distribution of the lines of current leaving the connecting cable all around the cathode. A cable 9 connects this shell with the other terminal of the capacity.

The rods 2 which constitute the striking electrodes are carried by two discs 10 made of an insulating material, located on both sides of the spark gap device and maintained spaced by means of cross members.

For the purpose of clarifying the drawings, only one of these discs is illustrated in FIG. 3.

Each of the electrodes 2 is connected with a cable 11 which supplies it with a very high intensity,

The anode 1 is carried by a shaft 12, each end of which is secured to an insulating support member 13.

The cathode 3 is carried by the shell 8, which is itself secured to insulating support members 14.

The insulating discs 10 carrying the striking electrodes 2 are centered on the shaft 12 of the anode.

The operation of the above-described sparker is as follows:

The supply voltage is applied between the anode 1 and the cathode 3 of the spark gap device at the instant of the sudden discharge of a condenser through the cables 7 and 9.

All the striking electrodes 2 are excited separately and in synchronism by a shock voltage through the cable 11.

A pilot spark is then generated at the level of each striking electrode, between this electrode and the anode or the cathode, each spark ionizing the space where it is produced. These different ionization points produce a local decrease in the disruptive potential and an arc is thus created between the plate 6 of each sector of the cathode 3 and the anode 1.

The are is interrupted when the voltage falls below the de-energization voltage which is very low, i.e. at the end of the discharge of the condenser.

A particular arrangement of the anode 1 is shown, by way of non limitative example only, in FIG. 3. In this embodiment, the anode 1 is constituted by a cylinder provided with several stages 1a, 1b, 10, having different diameters, this cylinder being slidable along the shaft 12 by means of a lever 15, whereby its position on this shaft can be located for example by means of a pawl and ratchet mechanism. The length of each stage substantially corresponds to the length of the segments of the cathode. The zones of connection between the different stages will advantageously have a conical shape, generally without marked edges, so as to prevent too sudden a striking of the spark at the passage from a stage to another.

Each stage corresponds to a different distance between anode and cathode (distance d d d FIG. 4) and thus to a different range of voltages of utilization the smallest distance between anode and cathode corresponding to the passage of the lowest voltages.

Such a device provides for easy switching in the range of the voltages of operation of the spark gap device. It is also possible to provide the device according to the invention with an ultra-violet lighting of the space between the electrodes in order to increase the stability of this device control.

It will also be possible to provide a forced stream of gas between the electrodes, so as to keep at a constant value the disruptive voltage, in case of operation at a high switching rate.

It is further possible to place the spark gap device in a container filled with an inert gas under pressure.

The spark gap device according to the invention exhibits numerous advantages:

It is of simple construction, in spite of an increase mechanical strength.

It can be used for a wide range of currents. It is sufficient for this purpose either to lengthen the device in the direction of its generatrices, or to increase its diameter, while keeping the same distance anode-cathode. It is possible to switch energies higher than 100,000 joules.

The plurality of striking points is favourable to the development of an ionized annular zone.

The internal partitioning of the cathode increases the stability of the discharge, by decreasing the effect of selfblowing out of the arc and of rotation of the lines of currents. It results thereform a lowering of the de-energization voltage.

It is known that in the field of the hyperfrequences, it is preferable to use coaxial conductors. The coaxial struc ture according to the invention is thus also favourable to high frequency switch.

The voltage of operation of this spark gap device can be adapted within a very broad range (up to 50 kv.), it is suflicient for this purpose to vary the diameter of the anode cylinder.

I claim:

1. Three-electrode spark gap device, for closing a circuit which is connected with a very high voltage electric generator and in which a very high intensity is established, said spark gap device including a cylindrical anode electrically connected with a first terminal of the generator, a cathode having the shape of a cylindrical ring surrounding said anode and coaxial therewith, said cathode including on its internal wall, along its generatrices, radial extensions formed of partitions each terminated by a plate, said spark gap device also including a striking electrode located in the space limited on the one hand by two radial planes passing along the edges of two consecutive plates and, on the other hand, by the annular segment of the cathode comprised between these planes, said striking electrode being more particularly located in the space limited by said annular segment, said radial planes and said plates and being connected with a generator providing a shock voltage.

2. Spark-gap device in accordance with claim 1, wherein said anode, said cathode nad said striking electrodes have substantially the same length.

3. Spark-gap device in accordance with claim 1, wherein said cylindrical cathode is electrically connected with a second terminal of said electric generator by means of a shell made of an electrically conductive material, said shell having a cylindrical internal wall in contact with the external wall of said cathode, and being connected with said second terminal through a conductive cable.

4. Spark-gap device in accordance with claim 1, wherein said cylindrical anode is centred on a longitudinal shaft carried by at least one insulating support member, the cylindrical cathode concentrical to said anode and located outside said anode being carried by said shell secured to at least one insulating support member, said striking electrodes being secured to at least one insulating support member which is fixed with respect to said anode, said striking electrodes being electrically connected with said generator providing said shock voltage.

5. Spark-gap device in accordance with claim 1, wherein said anode is constituted by a cylinder having a length greater than the cylinder of the cathode, said cylinder con References Cited UNITED STATES PATENTS 1/1952 Partiot 313198 X 2/1961 Coeterier 313217 X JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner U.S. C1.X.R. 

